Hey Seth,
A simpler way to do this is to append the iCode to the end of the URL being accessed. The iCode is the unique code for this individual stored in their record. It's returned by DE after successful login. You can parse the returned XML to retrieve it and set it as a session variable.
You can see how the iCode is appended to the end of the URL by using the default WebLink login page. For example, use it to log into Online Giving or Event Registration and then check out the URL.
Appending this code will prevent the WebLink application from asking for re-authentication.
Tara Coulson
Advocate, Customer Experience